1. Field of the Invention
This invention relates to a method and means for determining the angle of attack of an airfoil on an aircraft, and particularly to a method and means utilizing a fluidic amplifier operating in conjunction with a rotatable indicator dial to accurately indicate the angle of attack of an airfoil.
2. Description of the Prior Art
The prior art relating to this invention is believed to be found in Class 116, sub-classes 265 and 266; Class 23, sub-classes 178, 179 and 180; sub-class 27 AT. A search through the field of search indicated has resulted in the following eleven patents; U.S. Pat. Nos. 1,504,785; 2,008,885; 2,237,306; 2,352,955; 2,499,284; 2,637,294; 2,367,295; 2,923,152; 3,452,707; 3,548,854; and 3,630,169.
As will be seen from the prior art patents listed above, the prior art is repleat with many different methods and means for gauging and/or indicating the angle of attack of an airfoil or other type blade, such as a turbine blade. Thus, U.S. Pat. No. 1,504,785 relates to a device for indicating the attitude of an aircraft and utilizes the deep pressures acting on the upper and lower surfaces of the airfoil to operate a pair of diaphrams connected for displacement in response to variations in such pressure, a lever arm actuated by deflection of each diaphram, and a helix operatively engaged by the lever to affect rotation of the helix upon lateral displacement of the lever. An indicator arm on the helix cooperates with a graduated scale to indicate the attitude of the airplane.
U.S. Pat. No. 2,008,885 relates to an artificial horizon in which a quantity of liquid is contained within a capillary tube which is in turn connected to radially outwardly extending capillary tubes with orifices adjacent the outer ends of the wings of an aircraft. The pressure on the orifices is related to the attitude of the airplane and such pressures control the position of the fluid in the artificial horizon to thus simulate the attitude of the airplane in a visible way for the benefit of the pilot.
U.S. Pat. No. 2,237,306 relates to an angle of attack indicator for aircraft airfoil in which the standard pitot-static arrangement is used in combination with a conventional "yaw head". The pitot-static system is connected by appropriate tubing into a chamber having a diaphram connected to a spindle. The yaw head orifices are connected by appropriate tubes to a second chamber having a diaphram connected to a spindle. The spindles are interconnected in such a way that they operate an indicator needle on an appropriate angle of attack scale. Thus, while this device appropriately indicates the angle of attack, it does so by a structure that is completely different from the structure forming the subject matter of this invention.
U.S. Pat. No. 2,352,955 relates to an angle of attack indicator utilizing the conventional pitot-static system to derive impulses acting on two different diaphrams, the ratio of the impulse on the diaphrams being a measure of the angle of attack. Thus, while dynamic pressure from two separate points is applied to a mechanism, the mechanism to which such impulses are applied is completely different from the structure forming the subject matter of this invention.
U.S. Pat. No. 2,499,284 relates to a stall indicator device for airplanes and utilizes the dynamic pressure of air channeled into a bubble chamber, thus causing bubbles to continuously rise through the fluid in the bubble chamber and visible to the pilot. When the angle of attack of the airfoil increases to a critical angle, the bubbles cease and such cessation of bubbling is also visible to the pilot, thus warning him that a critical angle has been achieved.
U.S. Pat. No. 2,637,295 also relates to an angle of attack device for aircraft, but utilizes an unstable vane controlled by the impact of the airmass for pivotal movement to open and close a valve that admits air into a "motor" in the form of a flexible bladder. Expansion and contraction of the flexible bladder controls the position of laterally extending rods into or out of the line of vision of the pilot to alert him to a stall condition.
U.S. Pat. No. 2,637,294 is similar to the structure taught by U.S. Pat. No. 2,637,295 in that an unstable vane is utilized to control a valve that admits air to a warning device, in this case, the warning device being a whistle.
U.S. Pat. No. 2,923,152 relates specifically to a sensing device that presents a multitude of orifices to the air mass ahead of an airfoil but is devoid of any disclosure of structure for indicating angle of attack as a result of the impact of air on the separate orifices.
U.S. Pat. No. 3,452,707 utilizes the concept of a fluid amplifier in conjunction that the stall or shock sensor for aircraft. A pure fluid amplifier is utilized to power an indicator piston, thus indicating or reflecting a stall condition or shock wave. While a fluid amplifier is utilized, the structure taught by this patent is distinctly different from the structure forming the subject matter of this invention.
U.S. Pat. No. 3,548,854 also relates to an angle of attack device utilizing the principle of a fluid amplifier. Structurally, the device provides a plurality of apertures in the underside of the wing near the leading edge, the apertures being arranged in a series extending transversely of the airfoil and receiving predetermined distances from the leading edge as the series progresses. As the angle of attack increases, a segment of the air which would normally flow below the airfoil reverses its direction and flows over the top of the airfoil. The point at which this reversal occurs on the underside of the airfoil is at varying distances with respect to the leading edge of the airfoil. Each orifice in the underside of the wing is connected to a fluid amplifier. Additionally, a power stream of input air is admitted to the fluid amplifier and this stream of power fluid is channeled by the fluid amplifier to a predetermined output. When a signal is received from one of the apertures or orifices on the underside of the wing, the power stream is switched to a second output channel. The fluid amplifier is biased by commuting communicating part of the power fluid of the amplifier into a control channel. Each of the bias amplifiers is connected to an indicator which indicates the flow through the output channel and the readings of the indicators will give a digital readout of the angle of attack. Again, while the principle of fluid amplification is utilized in this device, the means by which it is utilized is completely different from the structure forming the subject matter of this invention.
Lastly, U.S. Pat. No. 3,630,169 relates to a stall warning indicator having no moving parts and mounted on the leading edge of an aircraft near the point of stagnation of airflow when the stall condition occurs. Structurally, the device utilizes a pair of orifices working in conjunction with the output of a transmitter of an acoustic wave or jet air stream. The orifices or detectors are connected to a differential sensor in such a manner that when the stagnation point passes the axis of the transmissions, the differential sensor produces a signal to warn of an impending stall.
It will thus be seen from the prior art described above that many and varied stall warning devices are represented by the prior art. The prior art patents noted and discussed above are obviously not the only patents that relate to this subject matter. These patents were selected as being representative of the prior art as it relates to the concept of method and means depicted in the invention forming the subject matter of this invention.
Accordingly, it is one of the important objects of the present invention to provide a method and means for indicating the angle of attack of an airfoil which utilizes the concept of fluidic amplification in conjunction with a meter capable of being mounted on the instrument panel of an airplane and which depicts the angle of attack of the wing of the airplane at a glance.
Another object of the invention is the provision of an angle of attack meter for aircraft that is simple in its construction, economical to manufacture and accurate in its representation of the angle of attack of the airplane.
Still another object of the invention is the provision of an angle of attack meter for aircraft that is applicable in either non-pressurized or pressurized airplanes.
Another object of the invention is the provision of an angle of attack meter for aircraft that utilizes directly the output from a fluid amplifier to deflect a card or pointer a predetermined amount correlated to the angle of attack of the aircraft.
Yet another object of the invention is the provision of an angle of attack meter for aircraft which utilizes the output from a fluidic amplifier to rotate a card through a predetermined angle of rotation representative of the angle of attack of the wing of the aircraft, which angle of rotation of the card may be depicted either directly by rotation of the card or electrically through impulses generated by rotation of the card and which are displayed digitally for the benefit of the pilot.
The invention possesses other objects and advantages, some or which, with the foregoing, will be apparent from the following description and the drawings. It is to be understood however that the invention is not limited to the embodiment illustrated and described, since it may be embodied in various forms within the scope of the appended claims. Furthermore this invention is not limited to determining the angle of attack of an airfoil, it can also be used for measuring the direction of flow of any fluid or gas.